Mankiw, Romer and Weil's (1992) finding of a cross-country relationship between savings rates, school enrolment and income levels is highly ambiguous.Their interpretation that it is consistent with an augmented Solow model depends on the implausible assumption that educational productivity is vastly higher in advanced countries than poor ones. On the alternative assumption of consistent educational productivity, their model is very close to an AK-type, but with rising educational costs producing a degree of conditional convergence.